Vinyl dispersion resins are dispersions of fine particles of vinyl polymers in a liquid medium. Dispersions of the polymer particles in plasticizers are called plastisols, and can exhibit thixotropic flow properties. These properties render the resins useful as coatings. The dispersions are applied to a surface under high shear conditions, such as through a spray-gun, and they remain on the surface once applied. The coated article is then heated to around 300.degree. F. to fuse the resin particles to provide a uniform protective coating. Such coatings are used in the automotive industry to seal joints between two pieces of metal.
To impart thixotropic flow properties to the resin, a cross-linked unsaturated carboxylic acid polymer can be added to an emulsion of the vinyl polymer as is discussed in U.S. Pat. No. 4,581,413. The vinyl polymer emulsion is usually at a high pH due to the presence of surfactants. Adding the polycarboxylic acid to this slurry can destroy the colloidal stability of the suspension. Thus, as is disclosed in the patent, the polycarboxylic acid polymer is usually neutralized with ammonium hydroxide. The mixture of vinyl resin and polycarboxylic acid is then dried to provide a powder which is then dispersed in the desired liquid to provide the vinyl plastisol.
In a coating use, prior to application an adhesion promoter is added to the plastisol. Unfortunately, certain adhesion promoters interact with the polycarboxylic acid or other acid present as a comonomer with the vinyl chloride monomer. This interaction decreases the effectiveness of the adhesion of the coating. Also, such mixtures do not adhere well to surfaces coated with a primer when fused at temperatures below 270.degree. F.
In view of such disadvantages, a thixotropic vinyl resin dispersion which is fusible at temperatures below 270.degree. F. but which can adhere to metal surfaces is desired.